Robert s



Patented Mar. 8, 1932 PATENT orrlc'a UNITED STATES ROBERT S. ARCHER, 01? LAKEWOOD, AND LOUIS W. KEMPF, OF CLEVELAND OHIO, AS-

: SIGNORS T'O ALUMINUM COMPANY OF AMERICA, 01? PITTSBURGH, PENNSYLVANIA,

A. CORPORATION OF PENNSYLVANIA ALUEINUM-SILICON ALLoYS No Drawing.

This invention relates to aluminum base alloys containing silicon, and has for an 1mportant object to provide alloys in Which the alloys.

I A further object of the invention is the provision of aluminum base alloys containing. silicon in which other physical properties 1 such as tensile strength are satisfactorily commensurate with the improved elongation. A still further object of the invention is the provision ofa' series of aluminum base alloys containing silicon in which'the elon- 1-3 gation can be suitably varied to a predetermined extent by a proper choice of the alloying constituents.

Another object of the invention is the provision of aluminum base alloys containing silicon which in cast or other fabricated form can be used under conditions subjecting the article to elevated temperatures and will at such temperatures retain a high proportion of the strength and hardness exhibited at 7 ordinary temperatures.

The aluminum base alloys containing silicon are characterized by low specific gravity which has made them both useful and desirable for many purposes. When applied to certain uses which give rise to exacting requirements their strength and hardness have not at all times proved adequate, and it has been found that these properties may be considerably improved by the addition of small quantities of magnesium, as described in the copending application of L. W. Kempf, Serial No. 463,576. For many purposes these latter alloys with magnesium have proved quite satisfactory but at times it becomes desirable to simultaneously obtain in an alloy the low specific gravity and the strength and hardness of the aluminum-silicon-magnesium alloys with an elongation improved to r an'extent not heretofore attained in related cast alloys of this class.

Application filed December as, 1930. Serial No. 504,422.

One of the inherent disadvantages which have restricted the use of aluminum base alloys containing silicon, with or without other all oying ingredients, has been the difficulty in finding alloys of this nature with satisfac; tory elongation and which can be readily cast. As the amount of silicon is increasd, say from about 2.5 per cent to about 14 per cent, the elongation decreases to a comparatively low figure. In adding even small amounts of magnesium to the ordinary aluminum-silicon alloys We have observed that although the strength and hardness are improved the elongation is not appreciably increased if at all. WVe have, however, discovered that if the amount of iron present as an impurity 'be controlled by restricting it to less than 014 per cent, a remarkable improvement is evidenced in the elongation not only without loss of strength but even with the strength increased. We have discovered in addition that small quantities of copper, up to about 1.50 per cent, will in the heat-treated condition materially increase both strength and elongation.

We have also found that alloys within the scope of our invention containing varying amounts of silicon and magnesium with or without the addition of small amounts of copper are amenable to marked improvement by heat treatments now well known in the art, consisting of, for example, heating the alloys at fromabout 500 C. to 575 C. for a number of hours, say from 2 to 20 hours, followed by quenching. 'Qhis treatment is usually known as the sohition treatment. Even after the alloys have been thus in proved by heatwtreatment it is observed that those alloys in which the iron content has been controlled as hereinbelow described show a material improvement in elongation and also usually in strength over the ordinary alloys of this nature in .which no effort has been made to confine the iron content betion is desired in an ordinary casting the sili con content should preferably be between 2.5

per cent and 6 per cent, small amounts of other ingredients such as magnesium and in some cases copper being added as required. Improved casting properties may be secured by making use of silicon contents between 6 per cent and 10 per cent. A series of widely used commercial alloys are found between 10 per cent silicon and about 14 percent silicon,

which oiier good strength and elongation, particularly when modified by such methods as outlined in United States Patents Nos. 1,387,900, 1,410,461 or 1,572,459. In these separate classes of alloys it will be found that the elongation can be markedly increased by keeping the iron'content less than 0.4 per cent.

Typical eli'ects of decreasing iron content on the elongation and tensile strength of aluminum base alloys containing silicon and magnesium are g sen in Table A below, obtained with a series of alloys each member of which contained about 7.5 per cent silicon and 0.3 per cent magnesium, with the iron content varying as shown. Tensile specimens from these alloys were cast in sand, heat-treated for 20 hours at 538 (3., and quenched in water, with the following results:

Table A Tensile cent strength Elongation aggi lbs. per in 2111.

sq. in.

0. 4 l so, 470 3. 7 per cent 0. Z 29, 630 4. 8 per cent 0. 15 l .11, 480 7. 1 per cent It is observed that there is a marked increase in elongation as the iron content is lowered and there is a substantial increase in tensile strength. Table C indicates the eliect of a lower iron content on the tensile strength and elongation of aluminum base alloys containing 10 per cent silicon, 0.2 per cent magnesium and 0.1 per cent copper, the iron content varying as shown. Tensile specimens were cast in sand, given a solution treatment at 552 C. and quenched in water. Precedin the casting of the alloys they were modified with an alkaline reagent by a process familiar to those skilled in the art and outlined in one of the United States patents numbered hereinabove, which consists, briefly, in introducing into the molten allow an alkaline reagent which refines the silicon constituent present in the alloy.

Table 0' T l Tensile ggg gfi strength Elongation l tent lbsper in 2 in. l sq. in. l l 0 60 28, 580 10. 2 per cent l 0 47 30, 740 14. 0 per cent 0 14 33, 270 18.7 per cent It will be noted that-although the elongation with the high iron content is very favorable (due to the modifying process), further improvement is obtained as the iron is decreased. Even though the elongation of the alloy decreases with increasing silicon the elongation can nevertheless be improved by the methods we outline. Although the alloys will show a distinct improvement on modification, especially in the higher silicon ranges,

we have discovered that an additional marked over a range of about 2.5 to 14 per cent silicon and 0.1

per cent to 3 per cent magnesium (prefera ly not more than about 0.5 per cent) by varying the copper from about 0.1

per cent (preferably not more than about 1.5 per cent), even when the iron content is considerably more than 0.4 per cent. If very good elongation is desired in an ordinary casting the silicon content should preferably be between 2.5 and 6 per cent. Improved casting properties may be secured by making use of silicon contents between 6 per cent and 10 per cent. A series of widely used commercial alloys are found between 10 per cent and 14 per cent silicon, which offer good strength and elongation, particularly when modified by such methods as outlined in United States Patents 1,387,900, 1,410,461,

Table D gives examples of the increase in strength, elongation and hardness effected by additions of copper, as shown by cast test specimens of an alloy containing about 7.0 per cent silicon, about 0.33 per cent mag- I nesium and about 0.16 per cent iron with the copper varying as shown in Table D below. These specimens were heated for 20 hours at 538 C. and quenched.

Table D Tensile Per cent strength Elongation Brinell copper lbs. per in 2 in. hardness 0.02 31, 480 7 1 per am as. 5 0. 77 33. 770 7 3 per cent 71. 8 1.26 38,160 7 lpercent 80.2

' 0.16 per cent iron with copper as shown in Table E below. Sand cast specimens were heat treated for 20 hours at 538 C. and

quenched.

Table E Tensile Per cent strength Elongation Brinell copper lbs. per in 2 in. hardness sq. in.

0. 02 25, 810 5. 0 per cent 58 0. 25 31, 630 10. 1 per cent 04 content on an aluminum baswlloy containing 5 er cent silicon,- 0.3 per cent magesium, and 0. 5 per cent copper, the iron varying as shown. Tensile specimens were cast in sand heated for 20 hours at 538v 0., and quenched in water.

A number of alloys were subjected to varying conditions of temperature to determine the effect on their physical properties, the results being largely influential in our choice of the particular alloy to use where the product is exposed to temperature elevated beyond the ordinary. In one variety of test the alloys were given a solution treatment and subsequently reheated for a certain time at a lower temperature. Physical properties were determined both after the solution treatment and after the reheating treatment. Of all the alloys tested under the so-called solution and stabilization treatments the alloys containing copper suilered the least deterioration. Increasing the copper content was effective in decreasing the softening caused by the stabilization treatment.

As an example two alloys were chosen which contained approximately 0.4 per cent iron, 5.0 per cent silicon and 0.5 per cent magnesium. The variation in copper content is shown in Table G below. Sand cast bars from the alloys were heated for 18 hours at 550 C., quenched and reheated for 6 hours at 315 C. The result of tests after the solu tion treatment and also after the stabilization heattreatment are shown in the table.

Table G Per cent Cu 0.14

Tensile strength lbs. per sq. in. after solution treatment Tensile strength lbs. per sq. in. after treatment at 315 C Loss in strength";

Two significant facts may be noted from the table. One is that the increase in copper content efi'ected an increase in tensile strength after the solution heat treatment. The other is that the secondary heat treatment had considerably less injurious effect on the alloy with the greater copper content.

In compounding the alloys it will be found advantageous to begin with aluminum ingot of high purity. It will be recognized that iron may be picked up in the melting processes and that in order to assure a final iron content of less than 0.4 per cent 1t may be Y necessary to start with aluminum ingot of composition if necessary. The other constituents may be added to the molten alumilower iron content than 0.4 per cent. Melting on holding pots may be of non-ferrous mum in the customary manner, the silicon and copper, for instance, by means of rlch alloys and the magnesium in the pure state, to

give the desired amount of these constituents in the final alloy, having .due regard to the copper content, if any, in the aluminum ingot and in scrap metal, or metal of previous melts, etc., that the foundry may desire'to use up. However, our invention does not require a set technique in compounding the alloy since this can well be varied to suit foundry practice.

It is to be understood that in the appended claims the term alloy is used as including the alloy in thgzcast condition whether cast in sand or in any other. type of mold, whether heat-treated or unheat-treated and whether modified or unmodified.

lVe claim: p

1. A heat treatable alloy composed chiefly of aluminum and containing silicon between about 2.5 and 14 per cent, magnesium between about 0.1 and 0.5 per cent, and copper between about 0.1 and 1.5 per cent.

2. An aluminum base alloy containing from about 2.5 per cent to about 14 per cent silicon, from 0.1 per cent to 0.5 per cent magnesium,

and from about 0.1 per cent to about 1.25 per.

cent copper, the iron content being less than about 0.4 per cent.

3. An aluminum base alloy containing from about 10 per cent to'abbut 1 1 per cent silicon,

from 0.1 per cent 0 about 0.5 per cent magnesium, and from about 0.1 per cent to about 1.25 per cent copper, the iron content being less than about 0. 1 per cent.

In testimony whereof we hereto aifix our signatures.

ROBERT S. ARCHER.

LOUIS W.. KEMPF. 

